.TH SASH 1
.SH NAME
sash \- stand-alone shell with built-in commands
.SH SYNOPSYS
.B sash [-c command] [-f fileName ] [-p prompt] [-q] [-a]
.SH DESCRIPTION
The
.B sash
program is a stand-alone shell which is useful for recovering from certain
types of system failures.
In particular, it was created in order to cope with the problem of
missing shared libraries or important executables.
.PP
.B Sash
can execute external programs, as in any shell.  There are no restrictions
on these commands, as the standard shell is used to execute them if there
are any non-wildcard meta-characters in the command.
.PP
More importantly, however,
is that many of the standard system commands are built-in to
.BR sash .
These built-in commands are:
.PP
.nf
     -ar, -chattr, -chgrp, -chmod, -chown, -cmp, -cp,
     -dd, -echo, -ed, -grep, -file, -find, -gunzip,
     -gzip, -kill, -ln, -ls, -lsattr, -mkdir, -mknod,
     -more, -mount, -mv, -printenv, -pwd, -rm, -rmdir,
     -sum, -sync, -tar, -touch, -umount, -where
.fi
.PP
These commands are generally similar to the standard programs with similar
names.  However, they are simpler and cruder than the external programs,
and so many of the options are not implemented.  The restrictions for each
built-in command are described later.
.PP
The built-in commands which correspond to external programs begin with a
dash character in order to distinguish them from the external programs.
So typing "ls", for example, will attempt to run the real
.B ls
program.
If "-ls" is typed, then the built-in command which mimics
.B ls
is called.
.PP
For the built-in commands, file names are expanded so that asterisks,
question marks, and characters inside of square brackets are recognised
and are expanded.
Arguments can be quoted using single quotes, double quotes, or backslashes.
However, no other command line processing is performed.
This includes specifying of file redirection, and the specifying of a pipeline.
.PP
If an external program is non-existant or fails to run correctly, then
the "alias" built-in command may be used to redefine the standard command
so that it automatically runs the built-in command instead.  For example,
the command "alias ls -ls" redefines "ls" to run the built-in command.
This saves you the pain of having to remember to type the leading dash
all of the time.
If many external programs will not run, then the "aliasall" command may
be useful to create multiple aliases.
.PP
The "help" command will list all of the built-in commands in
.B sash .
If an argument is given, it will list only those built-in commands
which contain the given argument as a sub-string.
Each built-in command is described below in more detail.
.PP
.TP
.B alias [name [command]]
If
.I name
and
.I command
are provided, this defines an alias for a command with the specified name
which executes the specified command with possible arguments.
Arguments containing wildcards can be quoted in order to defer their
expansion until the alias is invoked.
If just
.I name
is provided, then the definition
of the specified command alias is displayed.  If nothing is provided,
then the definitions of all aliases are displayed.
.TP
.B aliasall
This defines aliases for all of the built-in commands that start with
dashes to the corresponding names without the dashes.
This may be useful when the system is so corrupted that no external
programs may be executed at all.
.TP
.B -ar [txp][v] arfile [filename]...
List or extract files from an ar archive.
The arfile argument specifies a file name which contains the archive.
If no additional filenames are specified, then all files in the archive are
operated on.
Otherwise, only those archive members which have the same name 
as one of the additional filenames are operated on.
Filenames which do not appear in the archive are ignored.
Archives cannot be created or modified.
The archiver correctly handles 4.0BSD archives,
and understands both the SysV and 4.4BSD extensions for long file names.
The extended pseudo-BSD formats are not supported;
nor are the two antediluvian binary formats derived from V7 and earlier.
(The GNU archiver normally creates archives in the 4.0BSD format with
SysV extensions.)
.TP
.B cd [dirName]
If
.I dirName
is provided, then the current directory is changed to the
dirName.  If
.I dirName
is absent, then the current directory is changed
to the user's home directory (value of the $HOME environment variable).
.TP
.B -chattr [+i] [-i] [+a] [-a] fileName ...
Change the attributes of the specified files on an ext2 or ext3 file system.
Using a plus sign adds the specified attribute for the files.
Using a minus sign removes the specified attributes for the files.
The 'i' attribute makes a file immutable so that it cannot be changed.
The 'a' attribute makes a file append-only.
This command is only available on Linux.
.TP
.B -chgrp gid fileName ...
Change the group id for the specified list of files.  The
.I gid
can
either be a group name, or a decimal value.
.TP
.B -chmod mode fileName ...
Change the mode of the specified list of files.  The
.I mode
argument
can only be an octal value.
.TP
.B -chown uid fileName ...
Change the owner id for the specified list of files.  The
.I uid
can
either be a user name, or a decimal value.
.TP
.B -cmp fileName1 fileName2
Determines whether or not the specified file names have identical data.
This says that the files are links to each other, are different sizes,
differ at a particular byte number, or are identical.
.TP
.B -cp srcName ... destName
Copies one or more files from the
.I srcName
to the
.IR destName .
If more
than one srcName is given, or if destName is a directory, then all
the srcNames are copied into the destName directory with the same
names as the srcNames.
.TP
.B -dd if=name of=name [bs=n] [count=n] [skip=n] [seek=n]
Copy data from one file to another with the specified parameters.
The
.I if
and
.I of
arguments must be provided, so stdin and stdout cannot
be specified.  The
.I bs
argument is the block size, and is a numeric
value (which defaults to 512 bytes).
.I Count
is the number of blocks
to be copied (which defaults to end of file for the input file).
.I Skip
is the number of blocks to ignore before copying (seek is used
if possible, and the default is 0).
.I Seek
is the number of blocks to
seek in the output file before writing (and defaults to 0).  Any of
the numeric decimal values can have one or more trailing letters
from the set 'kbw', which multiplies the value by 1024, 512, and 2
respectively.  The command reports the number of full blocks read
and written, and whether or not any partial block was read or written.
.TP
.B -echo [args] ...
Echo the arguments to the -echo command.  Wildcards are expanded,
so this is a convenient way to get a quick list of file names in a directory.
The output is always terminated with a newline.
.TP
.B -ed [fileName]
Edit the specified file using line-mode commands.  The following
.B ed
commands are provided: = c r w i a d p l s f k z and q.
Line numbers can be constants, ".", "$", "'x", 
.RI / string /
and simple
arithmetic combinations of these.  The substitute command and the
search expression can only use literal strings.  There are some
small differences in the way that some commands behave.
.TP
.B exec fileName [args]
Execute the specified program with the specified arguments.
This replaces
.B sash
completely by the executed program.
.TP
.B exit
Quit from
.BR sash .
.TP
.B -file fileName ...
Examine the specified files and print out their file type.
This indicates whether the files are regular files or not,
whether they contain printable text or shell scripts,
are executables, or contain binary data.
.TP
.B -find dirName [-xdev] [-type chars] [-name pattern] [-size minSize]
Find all files contained within the specified directory
tree which meet all of the specified conditions.
The -xdev option prevents crossing of mount points.
The -name option specifies a wildcard pattern to match the last
component of the file names.
The -type option specifies that the files must have a type
matching the specified list from the set: f d c b p s l.
These represent regular files, directories, character devices,
block devices, named pipes, sockets, and symbolic links.
The -size option specifies that the files must be regular files or
directories which contain at least the specified number of bytes.
.TP
.B -grep [-in] word fileName ...
Display lines of the specified files which contain the given word.
If only one file name is given, then only the matching lines are
printed.  If multiple file names are given, then the file names are
printed along with the matching lines.
.I Word
must be a single word,
(ie, not a regular expression).  If -i is given, then case is
ignored when doing the search.  If -n is given, then the line
numbers of the matching lines are also printed.
.TP
.B -gunzip inputFileName ... [-o outputPath]
Uncompress one or more files that had been compressed using the
.I gzip
or
.I compress
algorithms.
If the -o option is not given,
then each of the input file names must have one of the
extensions ".gz", ".tgz", or ".Z",
and those files will be replaced by the uncompressed versions of those files.
The original files will be deleted after the output files have been
successfully created.
The uncompressed versions of the files have the same names as the original
file names, except for a simple modification of their extensions.
If an extension is ".tgz", then the extension is replaced by ".tar".
Otherwise, the ".gz" or ".Z" extension is removed.
.sp
If the -o option is given, then the input files will not be deleted,
and the uncompressed versions of the files will be created as specified
by
.IR outputPath .
If the output path is a directory, then the uncompressed versions of the
input files will be placed in that directory with their file names
modified as described above, or with the same name if the input file name
does not have one of the special extensions.
If the output path is a regular file, then only one input file is allowed,
and the uncompressed version of that input file is created as the output
path exactly as specified.
If the output path is a block or character device, then the uncompressed
versions of the input files are concatenated to the device.
.sp
This command is only available if
.B sash
was compiled to use the gzip library.
.TP
.B -gzip inputFileName ... [-o outputPath]
Compresses one or more files using the
.I gzip
algorithm.
If the -o option is not given,
then each of the input file names will be replaced by the compressed
versions of those files,
The original files will be deleted after the output files have been
successfully created.
The compressed versions of the files have the same names as the original
file names, except for a simple modification of the extensions.
If an extension is ".tar", then the extension is replaced by ".tgz".
Otherwise, the ".gz" extension is added.
.sp
If the -o option is given, then the input files will not be deleted,
and the compressed versions of the files will be created as specified
by
.IR outputPath .
If the output path is a directory, then the compressed versions of the
input files will be placed in that directory with their file names
modified as described above.
If the output path is not a directory, then only one input file is allowed,
and the compressed version of that input file is created as the output
path exactly as specified.
.sp
This command is only available if
.B sash
was compiled to use the gzip library.
.TP
.B help [word]
Displays a list of built-in commands along with their usage strings.
If a word is given,
then just those commands whose name or usage contains the word is displayed.
If a word is specified which exactly matches a built-in command name,
then a short description of the command and its usage is given.
.TP
.B -kill [-signal] pid ...
Sends the specified signal to the specified list of processes.
.I Signal
is a numeric value, or one of the special values HUP, INT,
QUIT, KILL, TERM, STOP, CONT, USR1 or USR2.
If no signal is specified then SIGTERM is used.
.TP
.B -ln [-s] srcName ... destName
Links one or more files from the
.I srcName
to the specified
.IR destName .
If there are
multiple srcNames, or destName is a directory, then the link is
put in the destName directory with the same name as the source name.
The default links are hard links.  Using -s makes symbolic links.
For symbolic links, only one srcName can be specified.
.TP
.B -ls [-lidFC] fileName ...
Display information about the specified list of file names.
The normal listing is simply a list of file names, one per line.
The options available are -l, -i, -d, and -F.
The -l option produces a long listing giving the normal 'ls' information.
The -i option displays the inode numbers of the files.
The -d option displays information about a directory, instead of the
files within it.
The -F option appends a slash or asterisk to the file name if the file
is a directory or is executable.
The -C option displays the file names in a multi-column format.
The width of the output is calculated using the COLS environment variable.
.TP
.B -lsattr fileName ...
Display attributes for the specified files on an ext2 or ext3 file system.
The letter 'i' indicates that the file is immutable and cannot change.
The letter 'a' indicates that the file is append-only.
Dashes are shown where the attributes are not set.
This command is only available on Linux.
.TP
.B -mkdir dirName ...
Creates the specified directories.  They are created with the
default permissions.
.TP
.B -mknod fileName type major minor
Creates a special device node, either a character file or a block
file.
.I Filename
is the name of the node.
.I Type
is either 'c' or 'd'.
.I Major
is the major device number.
.I Minor
is the minor device number.
Both of these numbers are decimal.
.TP
.B -more fileName ...
Type out the contents of the specified file names, one page at a
time.  For each page displayed, you can type 'n' and a return to go
to the next file, 'q' and a return to quit the command completely,
or just a return to go to the next page.  The environment variables
LINES and COLS can be used to set the page size.
.TP
.B -mount [-t type] [-r] [-s] [-e] [-m] devName dirName
Mount a filesystem on a directory name.
The -t option specifies the type of filesystem being mounted,
and defaults to "ext3" for Linux and "ffs" for BSD.
The -r option indicates to mount the filesystem read-only.
The -s option indicates to mount the filesystem no-suid.
The -e option indicates to mount the filesystem no-exec.
The -m option indicates to remount an already mounted filesystem.
The -m option is only available on Linux.
.TP
.B -mv srcName ... destName
Moves one or more files from the
.I srcName
to the
.IR destName .
If multiple srcNames are given, or if destName is a directory, then
the srcNames are copied into the destination directory with the
same names as the srcNames.  Renames are attempted first, but if
this fails because of the files being on different filesystems,
then copies and deletes are done instead.
.TP
.B -printenv [name]
If
.I name
is not given, this prints out the values of all the current
environment variables.  If
.I name
is given, then only that environment variable value is printed.
.TP
.B prompt [word] ...
Sets the prompt string that is displayed before reading of a
command.  A space is always added to the specified prompt.
.TP
.B -pwd
Prints the current working directory.
.TP
.B quit
Exits from
.BR sash .
.TP
.B -rm fileName ...
Removes one or more files.
.TP
.B -rmdir dirName ...
Removes one or more directories.  The directories must be empty
for this to be successful.
.TP
.B setenv name value
Set the value of an environment variable.
.TP
.B source fileName
Execute commands which are contained in the specified file name.
.TP
.B -sum fileName ...
Calculates checksums for one or more files.
This is the 16 bit checksum compatible with the BSD sum program.
.TP
.B -sync
Do a "sync" system call to force dirty blocks out to the disk.
.TP
.B -tar [ctxv]f tarFileName [fileName] ...
Create, list or extract files from a tar archive.
The f option must be specified, and accepts a device or file name
argument which contains the tar archive.
When creating, at least one file name must be specified to be stored.
If a file name is a directory, then all the files and directories
within the directory are stored.
Linked files and other special file types are not handled properly.
When listing or extracting files, only those files starting with
the specified file names are processed.
If no file names are specified, then all files in the archive are processed.
Leading slashes in the tar archive file names are always removed so that you
might need to cd to "/" to restore files which had absolute paths.
.TP
.B -touch fileName ...
Updates the modify times of the specifed files.  If a file does not
exist, then it will be created with the default protection.
.TP
.B umask [mask]
If
.I mask
is given, sets the "umask" value used for initializing the
permissions of newly created files.  If
.I mask
is not given, then the
current umask value is printed.  The mask is an octal value.
.TP
.B -umount [-f] fileName
Unmounts a file system.  The file name can either be the device name
which is mounted, or else the directory name which the file system
is mounted onto.
The -f option unmounts the filesystem even if it is being used.
The -f option is only available on BSD.
.TP
.B unalias name
Remove the definition for the specified alias.
.TP
.B -where program
Prints out all of paths defined by the PATH environment variable where the
specified program exists.  If the program exists but cannot be executed,
then the reason is also printed.
.SH OPTIONS
There are several command line options to
.BR sash .
.PP
The -c option executes the next argument as a command (including embedded
spaces to separate the arguments of the command), and then exits.
.PP
The -f option executes the commands contained in the file name specified
by the next argument, and then exits.
This feature can be used to create executable scripts for
.B sash
by starting the script file with a line similar to:
.nf
	#! /bin/sash -f
.fi
.PP
The -p option takes the next argument as the prompt string to be used
when prompting for commands.
.PP
The -q option makes
.B sash
quiet, which simply means that it doesn't print its introduction line
when it starts.
This option is also implied if the -c or -f options are used.
.PP
The -a option creates aliases for the built-in commands so
that they replace the corresponding standard commands.
This is the same result as if the 'aliasall' command was used.
.SH SYSTEM RECOVERY
This section contains some useful information about using
.B sash
with
.B lilo
to perform system recovery in some situations.
Similar concepts should exist for other boot loaders and operating systems.
.PP
When important shared libraries are being upgraded,
it might be a good idea to have
.B sash
already running on a console by itself.
Then if there is a problem with the shared libraries
.B sash
will be unaffected and you may be able to use it to fix the problem.
.PP
If a problem with the system shows up at boot time so that you cannot
enter multi-user mode and log in,
then you can first try booting into single-user mode by adding the
.I single
keyword after your kernel image name at the
.B lilo
prompt.
If you manage to reach a shell prompt, then you can run
.B sash
from that shell (if necessary).
One reason for doing this is that you might need to use the
.B -mount
command with the -m option to remount the root file system
so that it can be modified.
.PP
If you cannot reach the shell in single-user mode,
then you can try running sash directly as a replacement for the init process.
This is done by adding the
.I init=/bin/sash
keyword after your kernel image name at the
.B lilo
prompt.
When this is done, then the use of the
.B aliasall
command might be useful to reduce attempts to access the root file system
when running commands.
.PP
If your root file system is so corrupted that you cannot get
.B sash
to run at all, then you will have to resort to a system recovery floppy.
.SH WARNINGS
.B Sash
should obviously be linked statically, otherwise its purpose is lost.
.PP
Several other system commands might be necessary for system recovery,
but aren't built-in to
.BR sash .
.SH AUTHOR
.nf
David I. Bell
dbell@canb.auug.org.au
12 January 2004
.fi
